This is a "Comp Cams Shimmed Adjustable Camshaft Button" for a 1986 or 1987 Buick Grand National, T Type, Turbo T, or GNX 3.8 liter turbo V6. This is highly recommended, especially for a roller camshaft. Roller cam lobes are ground flat instead of tapered, like hydraulic or solid cams, COMP Cams provides a means of holding the cam back to the rear of the engine. Their cam buttons ride between the front of the timing gear and the back of the front cover and can be shimmed for proper endplay of the cam.
